Inside the machine...

The brain acts like a computer, where all our senses are processed, and stored. Medical experiments have reproduced memories by stimulating part of the brain. Therefore to explain how the mind works it is important to understand the significance of each structure of the brain

The physical brain is a grey coloured organ encased in the skull, composed of about 10 billion nerve cells, each linked to another and together responsible for the control of all mental functions. All human emotions, including love, hate, fear, anger, elation, and sadness, are controlled by the brain. It also receives and interprets the countless signals that are sent to it from other parts of the body and from the external environment.

The brain consists of two hemispheres, the left and the right each the size of a clenched fist. Each hemisphere is joined by a broad transverse of nerve fibres, called the corpus callosum. The corpus callosum is the slab of white nerve fibres that connects these two cerebral hemispheres and transfers important information from one to the other.

The core brain is the enlarged section of the spinal cord at the entry to the cranium, it is very much concerned with reflex actions, such as breathing and heart-rate etc. The medulla oblongata controls breathing and some of the reflexes required to control posture.

Cerebellum

The cerebellum is a structure which is important in co-ordinating movement, and adjusting movement according to the environment. Movements once learned appear to get programmed into the cerebellum and the become automatic, without any conscious involvement such as walking and writing etc. You may be consciously thinking about what you want to write, but not about how to write.

The cerebellum is essential to the control of movement of the human body in space. It acts as a reflex centre for the co-ordination and precise maintenance of equilibrium. Voluntary muscle tone—as related to posture, balance, and equilibrium—is similarly controlled by this vital part of the brain. Thus, all motor activity, from hitting a baseball to fingering a violin, depends on the cerebellum.

Thalamus

The thalamus appears to have two separate functions, one is to process and relay information to the cerebellum arising from sense receptors. It also deals with the degree to which the cortex is stimulated, hence controlling sleep and wakefulness.

It is the crucial relay station for incoming sensory signals and outgoing motor signals passing to and from the cerebral cortex. All sensory input to the brain, except that of the sense of smell, connects to individual nuclei (clusters of nerve cells) of the thalamus.

Hypothalamus

The hypothalamus is a complex structure and seems to have a great many functions, playing an important part in endocrine activity, motivation and emotion. It is involved in eating, drinking, sexual behaviour, sleeping and temperature control.

It acts as a control mechanism, when the body becomes over-active or the emotions become aroused, the hypothalamus re-establishes homeostasis.

The hypothalamus regulates or is involved directly in the control of many of the body's vital activities and drives that are necessary for survival: eating, drinking, temperature regulation, sleep, emotional behaviour, and sexual activity. It also controls visceral functions by means of the autonomic nervous system

Medulla oblongata

Within the medulla are the vital control centres for cardiac, vasoconstrictor, and respiratory functions, as well as other reflex activities, including vomiting. Damage to this structure usually results in immediate death.

One important structure which runs through and between a number of structures is the reticular activating system (RAS). The RAS acts as an alarm clock, awakening the cortex so that it can interpret the incoming sensory signals. Also the RAS can determine what signals should reach the cortex, or even if any should. This leads us to believe that the RAS has an important bearing on what we understand as "consciousness", a damaged RAS can lead to a permanent coma, to total lack of consciousness.

The limbic system

Collectively, portions of the thalamus, hypothalamus, hippocampal formation, etc make up a functional unit of the brain called the limbic system. These structures are linked together in a unique way by fibre pathways and, as a result, control multifaceted behaviour, including emotional expression, seizure activity, and memory storage and recall.

One important observation as far as hypnosis is concerned is that novel or new sensory input leads the limbic system to activate the cortex; while repetition of a stimulus over a period of time, which excites neither the reward or punishment centres, leads to no such activation of the cortex, what is referred to as habituation. On the other hand, if the stimulus causes either reward or punishment then the continued stimulus leads to more and more activation of the cortex. In other words, the response is reinforced.

Amygdala

The amygdala is closely associated with fear. It is located below the pituitary gland. The amygdala is the nucleus responsible for the lurch you feel in your stomach when you turn around in a dark alley and notice someone following you. It couples a learned sensory stimulus (man in ski mask in alley = danger) to an adaptive response (fight or flight). The amygdala evaluates threat without logical reasoning.

Inputs: the amygdala must get sensory input, and it must be fairly highly processed input to recognize the elements of a scene that signal danger. The association areas of visual, auditory, and somatosensory cortices are the main inputs to the amygdala.

Outputs: the amygdala must be able to control the autonomic system, to provoke such an instant sympathetic response. The main outputs of the amygdala are to the hypothalamus and brainstem autonomic centers, including the vagal nuclei and the sympathetic neurons.

The amygdala is also involved with mood and the conscious emotional response to an event, whether positive or negative. To this end, the amygdala is also extensively interconnected with frontal cortex, mediodorsal thalamus, and the medial striatum.

In those with PTSD the amygdala becomes highly activated when recalling traumatic memories. It is thought that the amygdala may store memories of fear in such a way that they can be accessed very quickly. Those with PTSD will often have an acute startle response.

Conversely, trauma survivors with no evidence of PTSD at all ("hero" archetypes) show very little amygdala activity when recalling traumatic events. The limbic system / pre frontal cortex areas seem to block the input signals. As a consequence the startle reflex may be reduced or may not be present at all.

Functions of the Cerebral Cortex

Physiologists and neurologists have mapped areas of the cerebral cortex to localise and define the regions that are responsible for motor movement, sensory processes, and memory and other cognitive functions.

A large part of the human cortex, the frontal area, is used for awareness, intelligence, and memory. For example, after a sensation, such as visualising a new object, is recorded, the memory is stored for a short term (or more permanently) within nerve cells in the brain. When the object is seen again, the memory is recalled and the object is recognised.